Charles Mackay would have scoffed at the idea that a crowd of people could know anything at all. Mackay was the Scottish journalist who, in 1841, published Extraordinaiy Popular Delusions and the Madness of Crowds, an endlessly entertaining chronicle of mass manias and collective follies, to which the title of my book pays homage. For Mackay crowds were never wise. They were never even reasonable. Collective judgments were doomed to be extreme. “Men, it has been well said, think in herds,” he wrote. “It will he seen that they go mad in herds, while they only recover their senses slowly and one by one.” Mackay’s take on collective madness is not an unusual one. In the popular imagination, groups tend to make people either dumb or crazy or both. The speculator Bernard Baruch, for instance, famously said: “Anyone taken as an individual is tolerably sensible and reasonable -- as a member of a crowd, he at once becomes a blockhead.” Henry David Thoreau lamented: “The mass never comes up to the standard of its best member, but on the contrary degrades itself to a level with the lowest.” Friedrich Nietzsche wrote, “Madness is the exception in individuals but the rule in groups,” while the English historian Thomas Carlyle put it succinctly: “I do not believe in the collective wisdom of individual ignorance.”

Perhaps the most severe critic of the stupidity of groups was the French writer Gustave Le Bon, who in 1895 published the polemical classic The Crowd: A Study of the Popular Mind. Le Bon was appalled by the rise of democracy in the West in the nineteenth century and dismayed by the idea that ordinary people had come to wield political and cultural power. But his disdain for groups went deeper than that.A crowd, Le Bon argued, was more than just the sum of its members. Instead, it was a kind of independent organism. ft had an identity and a will of its own, and it often acted in ways that no one within the crowd intended. When the crowd did act, Le Bon argued, it invariably acted foolishly. A crowd might be brave or cowardly or cruel, but it could never be smart. As he wrote, “In crowds it is stupidity and not mother wit that is accumulated.” Crowds “can never accomplish acts demanding a high degree of intelligence,” and they are “always intellectually inferior to the isolated individual.” Strikingly for Le Bon, the idea of “the crowd” included not just obvious examples of collective wildness, like lynch mobs or rioters. It also included just about any kind of group that could make decisions.

So Le Bon lambasted juries, which “deliver verdicts of which each individual juror would disapprove.” Parliaments, he argued, adopt laws that each of theft members would normally reject. In fact, if you assembled smart people who were specialists in a host of different fields and asked them to “make decisions affecting matters ofgeneral interest,” the decisions they would reachwould be no better, on the whole, than those “adopted by a gathering of imbeciles.”

Over the course of this book I follow Le Bon’s lead in giving the words “group” and “crowd” broad definitions, using thewords to refer to everything from game-show audiences to multibillion-dollar corporations to a crowd of sports gamblers. Some of the groups in this book, like the management teams in Chapter 9 are tightly organized and very much aware of their identities as groups. Other crowds, like the herds of cars caught in traffic that I write about in Chapter 7, have no formal organization at all. And still others, like the stock market, exist mainly as an ever-changing collection of numbers and dollars. These groups are all different, but they have in common the ability to act collectively to make decisions and solve prohlems—even if the people in the groups aren’t always aware that’s what they’re doing. And what is demonstrahly true of some of these groups—namely, that they are smart and good at problem solving—is potentially true of most, if not all, of them. In that sense, Gustave Le Bon had things exactly backward. if you put together a big enough and diverse enough group of people and ask them to “make decisions affecting matters of general interest,” that group’s decisions will, over time, be “intellectually (superior) to the isolated individual,” no matter how smart or well-informed he is.